This paper addresses whether there are productivity differences between men and women among blue-collar workers. We compare the wages under piece- and time-rate contracts of men and women working in the same occupation in the same establishment in three countries: the U.S., Norway, and Sweden. The findings are summarized in four points. First, the gender wage gap is smaller under piece- than under time-rate work. According to the interpretation put forth here, two thirds of the gap at the occupation–establishment level is due to productivity differences, while one third is not “accounted for”, but could be due to discrimination or experience or other factors. Productivity differences between sexes in typically male-dominated blue-collar industries are however very small, of 1– 3%: Sweden 1%, U.S. 2% and Norway 3%. Second, in age groups where women on average have extensive family obligations, the wage gap is larger than in other age groups. Third, under time-rate work, the wage gap is more or less independent of supposed occupation-based productivity differences between men and women, while under piece-rate work, the wage gap mirrors quite closely assumed productivity differences, with women receiving a wage premium in female-advantageous settings and a penalty in male-advantageous settings. Fourth, in contrast to Sweden, in Norway and the U.S. women sort more often into piece-rate work than men.